(1) Field of the Invention
The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to protect metal interconnect structures from fluorine evolving from adjacent dielecic layers.
(2) Description of Prior Art
The semiconductor industry is continually striving to increase device performance via decreases in RC delays. In addition, an objective of decreasing cost has led to the development of semiconductor chips comprised with sub-100 nm features, allowing a greater number of smaller chips to be obtained from a specific size starting substrate, thus reducing the processing cost of a specific chip. The use of high conductivity aluminum or copper, for metal interconnect structures, as well as the use of low dielectric constant, (low k), layers, have greatly contributed to the desired decreases in the RC, (resistancexe2x80x94capacitance), delays. An easily obtainable, low k layer, used in the sub-100 nm devices, is fluorinated silica glass, (FSG), featuring a dielectric constant as low as 2 to 3. However the fluorine radicals, contained in the FSG layer, can out diffuse during subsequent processing and attack adjacent metal lines, resulting in corrosion of, or unwanted resistance increases of, the high conductivity copper interconnect structures. One method used to protect the metal, or copper structures from fluorine attack is the use of a silicon rich oxide, (SRO), layer, used to line or coat the metal structures prior to deposition of the low k, FSG layer. The SRO layer also provides protection to the gate oxide during plasma processing used during subsequent intermetal deposition, (IMD), procedures. However to adequately protect the metal lines a thick SRO layer is needed, possibly filling the narrow spaces between metal structures, therefore leaving little space available for the low k FSG layer. Therefore the objective of using a low k layer between metal lines to reduce capacitance, is negated via the filling of these narrow spaces with a higher dielectric constant, SRO layer.
This invention will describe a novel procedure for forming SRO on the surfaces of high conductivity metal interconnect structure, however still leaving adequate space between the metal interconnect structures, for placement of the low k FSG layer. Prior art, such as Lee et al, in U.S. Pat. No, 5,756,396, describe spacer formation, applied to a metal line, however that prior art does not show the novel procedure described in the present invention in which three SRO layers are used to form the needed protection on the surfaces of metal lines, without filling the narow space between the metal lines.
It is an object of this invention to fill narrow spaces between metal interconnect structures with a low k layer.
It is another object of this invention to protect the metal interconnect strutures from fluorine radicals emitted from the low k layer, via use of silicon rich oxide, (SRO), layers formed on the surfaces of the metal structures.
It is still another object of this invention to use a combination of SRO deposition and etch procedures, to form the protective SRO layers and shapes on the surface of the metal interconnect structures, still however leaving adequate space between the metal interconnects structures for filling by a low k layer.
In accordance with the present invention a method of forming silicon rich oxide, (SRO), layers and shapes on the surfaces of metal interconnect structures, to protect the metal interconnect structures from fluorine radicals emitted from a low A, fluorinated silica glass layer, located in the spaces between metal interconnect structures, has been developed. After deposition of a metal layer, and an overlying, first SRO layer, a patterning procedure is employed to form the metal interconnect structures, comprised with an overlying capping SRO layer. A thin, second SRO layer is deposited, then subjected to a anisotropic, reactive ion etching, (RIE), procedure to form a thin SRO spacer on the sides of the SRO capped, metal interconnect sutures. A thin, third SRO layer is next deposited, conformally coating the SRO capped metal interconnect structures, and the SRO spacers, still leaving space between these structures. A low k, FSG layer is then deposited, filing the space between the metal interconnect structures, protected by, an overlying SRO capping layer, the thin SRO spacers, and the thin conformal SRO layer.